The Swiss city of Geneva lowered its alert level on Monday, police said, 18 days after it began a search for a number of people who officials said had possible links to terrorism.

A police statement said the Security and Economy Department of Geneva canton, or region, had decided to return to the alert level in place before Dec. 10, after consulting with federal authorities.

"A new assessment of the terrorist threat situation after the Christmas holidays justifies this decision," the statement said. "Moreover, all the recent events considered as potential targets, be they diplomatic, religious or commercial, are now over."

Geneva is home to the European headquarters of the United Nations, the Red Cross, and many banks and trading houses, and it has passport-free borders with France, where Islamist militants killed 130 people in attacks in Paris in November.

Geneva went on high alert after a suspicious Belgian-registered vehicle fled from a late-night police check and crossed the border into France, and foreign authorities sent a tip about a suspected Islamic State cell in the region.

Police said the threat had moved from "vague" to "precise," without elaborating, and the Swiss attorney general opened a criminal inquiry on the basis of a "terrorist threat in Geneva" against unknown persons.

Two sources told Reuters at the time that the U.S. Central Intelligence Agency had provided a photo of four men to Swiss authorities, saying they could be on Swiss territory.

The photo, published in Swiss newspapers, showed four bearded men seated, with their faces blurred and index fingers raised in the air.

On Dec. 12, Geneva prosecutor Olivier Jornot said there was no indication the men were on Swiss territory.

While searching for suspects, Geneva police arrested two Syrians after finding traces of explosives in their car, although no connection between the various strands of investigation had been established, Jornot said.